Carbon Dating/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby. A man, Tim, and his robot, Moby, are in their back yard. Moby is digging with a shovel. MOBY: Beep! TIM: What’d you find? Let me see! Moby holds out the skeletal remains of a fish. TIM: Oh. That’s Ewan. I buried him here in the yard two years ago. MOBY: Beep. TIM: Yeah, why don't you put him back! Tim holds up and reads from a typed letter. TIM: Dear Tim & Moby, How do scientists use carbon to date old fossils and stuff? From Streifenbeuteldachs. TIM: Scientists have lots of different ways to date fossils and artifacts. One of the most popular methods is carbon dating, or carbon-14 dating. MOBY: Beep? The caption “carbon dating” appears on the screen. TIM: Carbon-14 is a radioactive isotope of carbon. The caption “isotope” appears on the screen. Two atoms are shown. The one on the left is labeled “carbon-12” and the one on the right is labeled “carbon-14”. Each atom is depicted by a set of closely-packed small spheres. Some are white and some are orange. The collection of tightly-packed spheres is surrounded by a set of large cloud-like spheres. TIM: Isotopes are two atoms of the same element with different numbers of neutrons. The most common isotope of carbon is carbon-12, with six neutrons and six protons. The atom on the left grows to fill the screen. TIM: Carbon-14 has eight neutrons, and it’s radioactive. The image on the screen is replaced by a large version of the atom that was originally shown on the right. Two neutrons are added to the center mass. The scene shifts back to Tim and Moby in the back yard. MOBY: Beep? TIM: It’s nothing to be afraid of — radiation occurs naturally. About one in every trillion carbon atoms is a radioactive carbon-14 atom. That includes the carbon inside the bodies of all living things! A sketch of a Neanderthal man is shown. The picture zooms in on the head and the skull can be seen. It continues zooming until individual atoms can be seen. TIM: Carbon dating compares the amount of carbon-14 from, say, an old bone, to the amount that’s in a similar substance today. A scientist, holding a scalpel, is shown examining a skull. The scene then shifts back to the back yard. MOBY: Beep? TIM: Well, radioactive substances are unstable. That means they decay into different substances over time. When a carbon-14 atom decays, it gains one proton, becoming a stable nitrogen atom. The carbon-14 atom is shown again. A small particle is seen leaving the atom and disappears off the right side of the screen. The color of the atom changes from blue to purple. The label “nitrogen” then appears. TIM: In a group of carbon-14 atoms — like the ones in your body — half of them will go through this radioactive decay every 5,700 years. A collection of blue atoms is shown. Large numbers at the top of the screen count up very rapidly, ending with the number 5,700. As the numbers count up, some of the atoms change color from blue to purple. The caption “radioactive decay” appears when the number reads 5,700 and about half of the atoms are now purple. TIM: If you wait another 5,700 years, half the remaining carbon-14 atoms will have decayed, and so on. The numbers resume counting up and more atoms change color from blue to purple. The numbers stop at 11,400, at which point about three-quarters of the atoms are purple. TIM: The amount of time it takes for half of a radioactive substance to decay is called its halflife. The caption “half-life” appears. The view returns to Tim and Moby talking in the back yard. TIM: So carbon-14 has a half-life of 5,700 years. When a plant or animal is alive, the amount of carbon-14 in its system doesn’t change. MOBY: Beep? TIM: Well, yes, the carbon-14 in our living bodies is slowly changing into nitrogen. But we’re also constantly taking in new carbon-14 atoms when we eat and breathe. A picture of a wooly mammoth is shown, eating grass. TIM: Once a creature dies, though, it stops eating and breathing, so it doesn’t take in any more carbon-14. The mammoth slumps to the ground and dies. TIM: From that point on, the amount in its body decreases at a steady rate, with half of it disappearing every 5,700 years. The mammoth changes into a skeleton of an elephant. TIM: Scientists who study a lifeform’s remains can tell when it died by comparing the amount of carbon-14 that would have been in a living creature to the amount that’s left. A female scientist holding a note pad is shown studying a bone. Then, we return to Tim speaking in the back yard. TIM: Carbon-14 dating can only be used on the remains of living things, and it’s only accurate to about 60,000 years ago. Other radioactive isotopes can measure much older things, including non-living substances, like rocks. Using radioactive isotopes to date objects is called radiometric dating. MOBY: Beep? TIM: Well, Uranium-238 has a half-life of 4.5 billion years, so it can measure things that are as old as our planet! Moby bends down and picks up a fossil of a strange-looking creature. TIM: Uh . . . I don’t think that’s from our planet. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts Category:BrainPOP Engineering & Technology Transcripts